The present invention relates generally to a method of fabricating a semiconductor wafer, and more particularly to a method and apparatus for detecting presence of residual polishing slurry subsequent to polishing of a semiconductor wafer.
Semiconductor integrated circuits are typically fabricated by a layering process in which several layers of material are fabricated on a surface of a wafer. This fabrication process typically requires subsequent layers to be fabricated upon a smooth, planar surface of a previous layer. However, the surface topography of layers may be uneven due to an uneven topography associated with an underlying layer. As a result, a layer may need to be polished in order to present a smooth, planar surface to a subsequent processing step. For example, an insulator layer may need to be polished prior to formation of a conductor layer or pattern on an outer surface thereof.
In general, a semiconductor wafer may be polished to remove high topography and surface defects such as scratches, roughness, or embedded particles of dirt or dust. The polishing process typically is accomplished with a polishing system that includes top and bottom platens (e.g. a polishing table and a wafer carrier or holder), between which the semiconductor wafer is positioned. The platens are moved relative to each other thereby causing material to be removed from the surface of the wafer. This polishing process is often referred to as mechanical planarization (MP) and is utilized to improve the quality and reliability of semiconductor devices.
The polishing process may also involve the introduction of a chemical polishing slurry to facilitate higher removal rates, along with the selective removal of materials fabricated on the semiconductor wafer. This polishing process is often referred to as chemical-mechanical planarization or chemical-mechanical polishing (CMP). The chemical polishing slurry is generally an aqueous acidic or basic solution having a number of abrasive particles, such as silica (SiO2), alumina (Al2O3), or ceria (Ce2O3) particles, suspended therein. One common silicon polishing slurry includes silica particles in a colloidal suspension. The proportion of particles in such an exemplary slurry is typically from 1-15% by weight, with the pH of the slurry typically being from 8.0-11.5 (as controlled by the addition of an alkali such as NaOH, KOH, or NH4OH). Other slurries are also commonly utilized to polish other wafer materials such as metals.
While the use of a chemical slurry provides numerous advantages, certain concerns arise from the use thereof. For example, as described above, the chemical slurry includes, amongst other things, abrasive particles. Such abrasive particles must be completely removed from the wafer prior to subsequent processing thereof. In particular, if any particles remain on the wafer after a post-polishing rinse and/or cleaning process, such particles may create defects during subsequent fabrication processes thereby lowering manufacturing yields which undesirably increases costs of the integrated circuit.
Moreover, it is desirable to completely remove the abrasive particles associated with the slurry from the work tools associated with the fabrication process. For example, if slurry particles become embedded in the polishing pad associated with the polishing table, polishing efficiency may be adversely effected thereby undesirably increasing costs associated with manufacture of the integrated circuit devices.
It should be appreciated that it is generally difficult to detect presence of residual particles from the chemical polishing slurry. In particular, the abrasive particles utilized in typical chemical polishing slurries are generally between 20-200 nanometers in diameter. Presence of such small particles is generally extremely difficult to do without use of sophisticated, expensive laboratory equipment such as a scanning electron microscope (SEM). It should be appreciated that use of such laboratory equipment is impractical for use in a manufacturing process due to the amount of time necessary to test a single specimen.
Thus, a continuing need exists for a method which accurately and efficiently detects presence of residual chemical slurry subsequent to a chemical-mechanical polishing process. Moreover, a continuing need exists for a method which accurately and efficiently detects presence of residual chemical slurry subsequent to a chemical-mechanical polishing process which can be quickly and easily incorporated into a manufacturing process.
In accordance with one embodiment of the present invention, there is provided a method of detecting presence of a polishing slurry subsequent to polishing of a semiconductor wafer. The method includes the step of adding a chemical marker to the polishing slurry. The method also includes the step of polishing a first side of the wafer in order to remove material from the wafer. The method further includes the step of applying the polishing slurry to the first side of the wafer during the polishing step. Moreover, the method includes the step of ceasing the polishing step when the wafer has been polished to a predetermined level. Yet further, the method includes the step of detecting presence of the chemical marker so as to determine presence of the polishing slurry subsequent to the ceasing step.
Pursuant to another embodiment of the present invention, there is provided a method of detecting presence of a polishing slurry on a semiconductor wafer subsequent to polishing of the wafer. The method includes the step of adding a chemical marker to the polishing slurry. The method also includes the step of polishing a first side of the wafer in order to remove material from the wafer. In addition, the method includes the step of applying the polishing slurry to the first side of the wafer during the polishing step. Moreover, the method includes the step of ceasing the polishing step when the wafer has been polished to a predetermined level. Yet further, the method includes the step of directing incident electromagnetic radiation onto the wafer subsequent to the ceasing step. The method also includes the step of detecting a physical characteristic of resultant electromagnetic radiation which is produced in response to the incident electromagnetic radiation being directed onto the wafer. Moreover, the method includes the step of determining presence of the chemical marker so as to determine presence of the polishing slurry on the wafer based on the physical characteristic of the resultant electromagnetic radiation.
Pursuant to yet another embodiment of the present invention, there is provided a method of detecting presence of a polishing slurry on a work tool subsequent to polishing of a semiconductor wafer. The method includes the step of adding a chemical marker to the polishing slurry. The method also includes the step of polishing a first side of the wafer with the work tool in order to remove material from the wafer. The method further includes the step of applying the polishing slurry to the first side of the wafer during the polishing step. Moreover, the method includes the step of ceasing the polishing step when the wafer has been polished to a predetermined level. In addition, the method includes the step of directing incident electromagnetic radiation onto the work tool subsequent to the ceasing step. Yet further, the method includes the step of detecting a physical characteristic of resultant electromagnetic radiation which is produced in response to the incident electromagnetic radiation being directed onto the work tool. Moreover, the method includes the step of determining presence of the chemical marker so as to determine presence of the polishing slurry on the work tool based on the physical characteristic of the resultant electromagnetic radiation.
Pursuant to yet a further embodiment of the present invention, there is provided a polishing system for polishing a semiconductor wafer. The polishing system includes a polishing station which is operable to remove material from the wafer. The polishing station has a polishing surface which contacts a first surface of the semiconductor wafer so as to remove the material therefrom. The polishing system also includes a slurry distribution assembly for advancing a polishing slurry onto the polishing surface. The polishing slurry has a chemical marker present therein. The polishing system further includes a rinse station which is operable to direct a flow of fluid onto the wafer subsequent to polishing by the polishing station. Moreover, the polishing system includes a slurry detection station which is operable to detect presence of the chemical marker so as to determine presence of the polishing slurry on the wafer after the flow of fluid has been directed onto the wafer by the rinse station.
It is an object of the present invention to provide a new and useful method and apparatus for detecting presence of residual polishing slurry subsequent to a chemical-mechanical polishing process.
It is also an object of the present invention to provide an improved method and apparatus for detecting presence of residual polishing slurry subsequent to a chemical-mechanical polishing process.
It is a further object of the present invention to provide a method and apparatus for detecting presence of residual polishing slurry on a semiconductor wafer subsequent to a chemical-mechanical polishing process.
It is yet further an object of the present invention to provide a method and apparatus for detecting presence of residual polishing slurry on a work tool subsequent to a chemical-mechanical polishing process.
It is also an object of the present invention to provide a method and apparatus for detecting presence of residual polishing slurry subsequent to a chemical-mechanical polishing process which can be quickly and easily integrated into a manufacturing process without the need for expensive laboratory equipment.
The above and other objects, features, and advantages of the present invention will become apparent from the following description and the attached drawings.